test: dm: spi: Replace _spi_get_bus_and_cs() by spi_get_bus_and_cs() in some case

In case _spi_get_bus_and_cs()'s parameters drv_name and dev_name are
respectively set to NULL and 0, use spi_get_bus_and_cs() instead.

Signed-off-by: Patrice Chotard <patrice.chotard@foss.st.com>

Cc: Marek Behun <marek.behun@nic.cz>
Cc: Jagan Teki <jagan@amarulasolutions.com>
Cc: Vignesh R <vigneshr@ti.com>
Cc: Joe Hershberger <joe.hershberger@ni.com>
Cc: Ramon Fried <rfried.dev@gmail.com>
Cc: Lukasz Majewski <lukma@denx.de>
Cc: Marek Vasut <marex@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
Cc: Simon Glass <sjg@chromium.org>
Cc: Stefan Roese <sr@denx.de>
Cc: "Pali Rohár" <pali@kernel.org>
Cc: Konstantin Porotchkin <kostap@marvell.com>
Cc: Igal Liberman <igall@marvell.com>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Pratyush Yadav <p.yadav@ti.com>
Cc: Sean Anderson <seanga2@gmail.com>
Cc: Anji J <anji.jagarlmudi@nxp.com>
Cc: Biwen Li <biwen.li@nxp.com>
Cc: Priyanka Jain <priyanka.jain@nxp.com>
Cc: Chaitanya Sakinam <chaitanya.sakinam@nxp.com>